Tankless Water Heaters Waste Water – It’s a Fact!

Australia is suffering a terrible drought, and as a result they are very concerned about conserving water.  This is no doubt why The Australian Department of the Environment, Water, Heritage and the Arts conducted a series of tests to determine how much water was wasted by tankless water heaters.

A wide variety of tankless heaters were tested

They tested 8 models of gas tankless water heaters ranging in capacity from 4.2 gallons per minute to 8.45 gallons per minute.  The heaters were various brands and some were indoor models and some were outdoor models.

The testing concluded that tankless water heaters waste water

The study concluded that tankless water heaters waste "substantial" quantities of water.  It was found that it generally takes about a gallon of water passing through the heater for the temperature to reach within a couple of degrees of the set point.   The time required varied widely with flow rate and heater size, ranging from about 10 seconds to over a minute.  That is waiting time over and above the waiting time for a tank type heater in the same piping layout.

A copy of the study can be found at the website of the Alliance for Water Efficiency in their resource library.

Hot water circulating systems

Traditional hot water circulating systems will not work with a tankless water heater, but hot water demand pumping does work and should be used if water wastage is to be minimized.

Hot water demand systems are similar to the older full-time circulating systems, but they only pump enough water to fill the pipe to the fixture with hot water, then they shut off.  These systems can use either a dedicated return line, or use the cold water line as the return.  Since the pump shuts off when hot water reaches it, little if any warm water ends up in the cold water line.

With a demand system, the user presses a button to start the pump, and an internal temperature sensor shuts the pump off when hot water reaches it. The user can then turn on the hot water fixture and obtain nearly instant hot water without having run any water down the drain.

Typically these demand pumps use less than about $2.00 in electricity per year to operate, and no more energy is used by the water heater than if the pump wasn't installed. Some models can be purchased for less than $200. Manufactures of these systems include Chilipepper Sales, ACT Metlund Systems, and TACO pump Inc.

Water wastage is behaviorally driven

The amount of water you waste is a behavior driven figure, depending heavily on how the hot water is being used.  For instance, if you seldom use hot water, then if you have a tank type water heater, your energy consumption will be mainly from standby losses, and you are a better candidate for a tankless heater.

If you use hot water frequently and in large quantities your standby losses will be much smaller in relation to the total energy consumption.  But those cases might also be the ones where you would need a tankless unit to avoid running out of hot water.

Machines don't waste hot water...Humans do

Machines don't waste water since they just take what's available at the inlet to the appliance. However, in those cases you might prefer to have a demand hot water system since the most common reason for poor dishwasher performance is too low of a water temperature.  This is due to the dishwasher's limited water draw, often most of which is cooled-off hot water.

When the water isn't hot enough the soap doesn't completely dissolve, leading to complaints.  Many dishwashers heat the water with a heating element if it isn't hot enough, and this is a very expensive way to heat water if your water heater is gas.

Hot water demand systems are green products

If you have long pipe runs and a tank type heater, then you are already probably wasting a lot of hot water. A tankless water heater makes it that much worse. In either case adding a hot water demand system reduces your water wastage, and that is good for you and for the environment.